"We document everything," Harran told ABC News in a telephone interview Thursday.
The majority of the police contacts with the now 20-year-old DiNardo, a Bensalem resident, involved calls about: concerns over his mental health, domestic incidents, DiNardo's alleged improper riding of an ATV, and traffic citations. Other police contacts with DiNardo included when there was a report of a suspicious vehicle and disturbance at his high school and DiNardo, who was allegedly behaving in a loud and disorderly manner on school grounds, was asked to leave, according to Harran.
But none of these prior encounters resulted in any arrests of DiNardo, police said.
DiNardo's first arrest came Monday, July 10, the same day that authorities investigating the disappearances of four young men executed a search warrant at a vast Solebury Township property owned by DiNardo's parents.
DiNardo was arrested that day on a charge stemming from illegally possessing a shotgun and ammunition back in February. The following day, July 11, he was named a person of interest in connection with the men's disappearances but was released from jail after meeting bail.
The day after that, July 12, DiNardo, facing accusations that he had taken the car of one of the missing men, Thomas Meo, was taken back into custody.
Subsequently both DiNardo and Sean Kratz, 20, of Philadelphia, who was also arrested, were charged with criminal homicide in the July 7 deaths of Dean Finocchiaro, 19, of Middletown Township, Meo, 21, of Plumstead Township, and Mark Sturgis, 22, of Pennsburg.
Investigators found the bodies of the three men Wednesday in a roughly 12-foot-deep grave on a sprawling property in Solebury Township owned by DiNardo's parents, according to the Bucks County District Attorney's Office.
DiNardo is also accused of killing Jimi Tar Patrick, 19, of Newtown Township, on July 5, and burying him in a single grave elsewhere on the same property.
Both men have pleaded not guilty to the charges against them.
According to court documents obtained by ABC News, DiNardo told detectives he used a backhoe to dig both graves.
Patrick went missing July 5, while Finocchiaro, Meo and Sturgis all disappeared July 7. All four men were shot and each victim has been positively identified. Their family members have been briefed on details of the case, according to the district attorney's office.
Court documents show DiNardo and Kratz also face multiple counts of conspiracy, robbery and abuse of a corpse.
DiNardo and Kratz have each provided statements to investigators, and DiNardo has described Kratz as his cousin, according to the district attorney's office.
At a July 14 news conference, Bucks County District Attorney Matthew Weintraub said he made an "agreement" with DiNardo that allowed investigators to locate Patrick's body, which was buried as far as a half-mile away from where the three other bodies were found. The agreement includes not seeking the death penalty, Weintraub said.
When asked about a motive, Weintraub told reporters, "I don't know that, and I'm not sure we'll ever know."
DiNardo and Kratz were arraigned July 14 before Magisterial District Judge Maggie Snow of Buckingham Township. Neither were able to post bail. They are scheduled for a July 31 preliminary hearing before Snow.
Harran also said there was no way to have known from DiNardo's prior contacts with law enforcement that he would later be accused of horrific murders.
The public safety director added, however, that the police department had not been aware of DiNardo's prior, court-ordered mental health treatment.
“The lack of coordination on mental health is a problem in this country,” Harran told ABC News.
“There’s no database to tell us he was 302’d,” he added, using a Pennsylvania legal term for court-ordered mental health treatment. “There are [others] walking all over the streets. I’ve got six more like him.”
In hindsight, Harran said, "Maybe [DiNardo] should have been in for a little bit longer than he was in for, as far as mental health."
Regardless, Harran said it's crucial for law enforcement to be made aware when someone they've received calls about repeatedly is evaluated for potential psychiatric issues. In DiNardo's case, Harran said there were clues that "the guy's got problems" but police did not know enough to realize he may later be charged with killing.
“There’s a gap,” Harran told ABC News. “And we’re always the ones holding the bag. We’re out here dealing with people. People are always afraid of information police are going to learn about them. It’s not like we open up a phone book and start running people. We don’t have time for that. We only look at it when we need it.”
One of DiNardo's defense attorneys, Paul Lang, told reporters last week that DiNardo confessed to killing the four men and gave authorities the location of the bodies.
The motive for the killings will come out in time, the lawyer said.
DiNardo felt "deep remorse" and is "very emotional," Lang told ABC News.
ABC News' Michael Claiborne, Gregory Croft, Michael Del Moro, Eva Pilgrim and Stephanie Wash contributed to this report.