Philadelphia police are asking the public for help in solving three sexual attacks in the Northeast over the last two months that they say could be related.

At a news conference Friday, Capt. John Darby of the Special Victims Unit said there were similarities in all three assaults, which happened within a dozen blocks of one another between April 25 and May 28.

In all three cases, the women were walking on city streets at night alone when a man approached from behind and grabbed them. They described their attacker as white, in his mid-20s, about six feet tall with a thin or medium build.

"We need the community to step up and say, 'We're not going to allow this to happen in our neighborhood.' We're doing everything we can," Darby said, "so we definitely need the public's help."

Police said the most recent attack happened about 10:30 p.m. Wednesday in the 6700 block of Roosevelt Boulevard, the Castor Gardens section of the Northeast. A 20-year-old woman was walking alone when a man grabbed her and knocked her to the ground. He then forced her in back of a building and sexually assaulted her, police said.

On May 17 in the 3200 block of Wellington Street in Mayfair, a 29-year-old woman was on her way home when she was grabbed from behind. The man put an object to her neck and tried to remove her clothes, but a neighbor alerted by noise intervened, and the attacker fled, police said.

The first attack also happened in Mayfair, about 11:45 p.m. April 25. A woman was walking in the 3300 block of Tyson Avenue when a man came from behind and put an object to her neck. He then took the woman to a rear driveway in the 3300 block of Disston Street, where he assaulted her, police said.

Police ask anyone with information about the attacks to call the Special Victims Unit at 215-685-3251.

On Saturday, members of the Philadelphia Police Explorer Cadet Program will assist the Special Victims Unit by passing out bulletins about the sexual assaults in the 15th Police District in areas from Frankford to Brous Avenues and Princeton to Bleigh Avenues.