Missing from the mall: How investigators nabbed a serial rapist in the death of a college student

More than 20 years ago a North Dakota town was shaken after a college student went missing after she left the mall where she worked at the beginning of the busy holiday season.

Dru Sjodin's disappearance in November 2003 banded together several of her friends, family, and neighbors in two states along with multiple law enforcement agencies.

And although their search ended in tragedy, her family was able to get justice and spark change to make it easier for the public to track sex offenders living in their communities.

A "20/20" episode airing Jan. 12 at 9 p.m. ET and streaming on Hulu the next day takes a look at the case with interviews with key investigators, Sjodin's family, college friends, and others.

Dru Sjodin, 22, who was a senior at the University of North Dakota studying graphic arts, was leaving her job at the Columbia Mall in Grand Forks on Nov. 22, 2003. After buying a purse at one of the stores, she walked to the parking lot and was on the phone with her boyfriend Chris Lang, according to investigator Bill Macki.

"That phone call was interrupted and she abruptly hung up," Macki told "20/20." "Prior to doing so, she said something along the lines of 'OK, OK.'"

Lang would later get another call from her number three hours later but could only hear static and the sound of the dial pad being typed, investigators said.

Dru Sjodin's friends would call the police after they found out she didn’t show up at her second job later in the night. Officers found her car still in the parking lot and a knife sheath near one of the tires.

Allan Sjodin said he immediately drove to the town after getting word that his daughter was missing

He said when he got to the parking lot and saw her car, he was so taken with emotion that he held a vigil next to the vehicle, hoping his daughter would return to her car.

"It was a God-awful terrible night," he said.

Investigators were soon able to track the location of the second phone call to Lang, which was near Crookston, Minnesota.

Because of the likelihood that the young college student was abducted and transported across state lines, more law enforcement agencies, including the FBI became involved in the case and searched the area, which at this point of the year was covered in snow.

One of Dru Sjodin’s shoes was found under a bridge in Crookston, roughly 25 miles away from the mall.

As search teams combed the area for any more signs of the missing college student, investigators hit the ground looking for potential suspects.

Four days after Dru Sjodin went missing, investigators received a tip from someone who claimed they saw a known sex offender shopping in Grand Forks the day she disappeared.

When investigators started to look into the criminal history of that man, Alfonso Rodriguez Jr., they said they feared they had a serial rapist on the loose.

In 1974, Rodriguez was convicted of aggravated rape and attempted aggravated rape in conjunction with attacks on two young women.

Shirley Iverson, Rodriguez's first victim, told "20/20" that he assaulted her after she agreed to give him a ride home after recognizing him as a fellow student from school.

"Being held against your will, and then to be, you know, sexually assaulted combines the two worst fears that you have," she said.

In his second assault, Rodriquez used a kitchen knife to threaten his victim, according to court papers.

He was sentenced to 15 years in prison in one case, but the sentence was stayed, and he was sentenced to the Minnesota Security Hospital for sex offender treatment in the other case.

In 1980, Rodriguez struck again when he was on leave from the hospital to visit family, investigators said. He attempted to kidnap a woman and stabbed her twice before she fought him off and fled.

Rodriguez served 23 years in prison after the third assault and after he was ordered to serve his previously stayed sentence. He was released in May 2003.

Investigators picked up Rodriquez and questioned him on Nov. 26, 2003. He admitted that he was in Grand Forks four days earlier to shop for clothes and claimed he also saw a showing of the movie "Once Upon a Time in Mexico."

Investigators said the movie was not being played at the times that Rodriguez claimed he saw it.

Rodriguez allowed investigators to search his car. Special Agent Daniel Ahlquist of the Minnesota Bureau of Criminal Apprehension told "20/20" that knives were found in the trunk and glove compartment of the vehicle.

At the same time, crime scene experts examined the knife sheath that was found next to Sjodin's car and determined it was part of a set that came with a folding knife typically sold at Menards.

"They showed us the knife that was associated with the sheath. And you could have knocked me over with a feather because I had just seen that exact knife in Alfonso’s trunk," Ahlquist said.

Rodriguez provided the knife to investigators when they asked and came down to the station for further questioning. He denied being involved with Dru Sjodin's disappearance.

A search of Rodriguez's car found blood specks on the rear window and back seat which later matched the missing woman's DNA.

"I believe that she may have been hit in the face or something that caused bleeding," Ahlquist said.

As the search crews continued to look for Dru Sjodin's body, police arrested Rodriguez and charged him with kidnapping.

Five months of searches by police, neighbors and others turned up no sign of the missing woman but on April 17, 2004, Dru Sjodin's family would get tragic news.

Her body was found in a ravine that was just under freshly melted snow just outside of Crookston. She was naked from the waist down with her hands bound behind her back.

"It was absolutely a horrible day, but it was, it was a day of um, a day of relief at, cause at that point we, you know, knew that Drusie was no longer with us," Allan Sjodin said.

Because Dru Sjodin's case took place across state lines, it became a federal case and Rodriguez was eligible for the death penalty. He was convicted of a kidnapping resulting in death charge on Aug. 30, 2006.

Rodriguez was sitting on death row for 15 years when the judge who issued the sentence overturned the death penalty in an appeal ruling. Judge Ralph Erickson cited numerous factors including issues with the medical examiner's testimony and a failure by Rodriguez’s defense team to pursue an insanity defense.

In March, federal prosecutors announced that they would not pursue the death penalty as federal executions were put on hold by the Dept. of Justice.

"Right now, he’s serving life in prison without the possibility of parole," Tom Heffelfinger, the former U.S. Attorney for the District of Minnesota, told "20/20."

Dru Sjodin's memory and legacy would be felt for years to come. Her school set up a scholarship in her name and Congress would name the National Sex Offender Public Website after Dru Sjodin which allowed states to share their data.

Her father said he still listens to the final voicemail she left on his phone and remembers the good she brought into people's lives.

"She had a huge heart, she had a beautiful smile and she was just a fantastic young lady that went way, way too soon," Allen Sjodin said.