"The suspects returned to the scene of the crime, removed the rugs and linoleum, cleaned the rooms and repainted the walls," Kelly said. "They could clean, but they couldn't hide."
Investigators said they found alcohol cans and hair at the scene.
An onlooker also slipped a phone number to detectives, leading them to the primary suspect, Kelly said.
The alleged victims were initially reluctant to talk to police, but eventually started to give details about the assaults, Kelly said.
The Hate Crimes Task Force took over the investigation, along with Bronx robbery and gang division and special victims squad, and arrested the seven men.
The mother of one of the suspects told ABC New York station WABC-TV that she cannot believe that her son could be involved in such a heinous crime.
"That would surprise me for real, because I can't picture my son doing something like that," Kramer said.
City Council Speaker Christine Quinn, the city's highest-ranking openly gay official, called the attacks "vile" and "horrifying."
"These attacks are appalling and are even more despicable because the victims were clearly targeted in acts of hate simply because they are gay," Quinn said. "The cowardly few who committed these crimes do not represent New Yorkers, and our community will not be cowed by such violence."
A weekend rally on anti-gay bias was planned following other crimes against gays.
On Sunday, a patron at the Stonewall Inn, a symbol of the gay rights movement since protests over a 1969 police raid there, was beaten in an anti-gay bias attack, according to prosecutors.
Two suspects in the case were charged. Their attorneys say they're not guilty.
That attack followed the Sept. 22 death of New Jersey college student Tyler Clementi, who jumped off the George Washington Bridge after his sexual encounter with a man in his dorm room was secretly streamed online. The student's roommate and another freshman have been charged with invasion of privacy. Authorities are considering bias-crime charges.
The attacks remain all too common, and there is still a stigma to being a lesbian, gay, bisexual or transgendered person, said Sharon Stapel, executive director of the New York City Anti-Violence Project, which works to combat attacks on gays and others.
"We have to stop thinking that it's OK to bully LGBT people or make fun of LGBT people," Stapel said.
"What we see now is the link between casual sort of comments and the real and horrific violence that results because those comments contribute to an entire culture of violence," she said.
In a statement on the incident Bronx borough President Ruben Diaz Jr. said: "Bronxites will not tolerate any form of bigotry in our borough, and we stand together as 1.4 million residents to condemn these actions and to oppose hatred in all its forms."
The Associated Press contributed to this report.