For police, the 130th, 131st and 132d slayings in Philadelphia stand out from the pattern that has defined homicide in the city in recent years.

The victims were female and they were killed indoors, two of them with a knife, at a time when most of those slain are males, shot on the street. And police identified suspects quickly in the cases.

In the 130th homicide, a 16-year-old mother of a 10-month-old girl was shot in the head late Wednesday night over what one top police official called "even less than an argument" in a house full of people in the Mill Creek neighborhood of West Philadelphia.

And at 6 a.m. today, a neighbor found two women stabbed to death in their second-floor apartment in an increasingly Asian section of South Philadelphia.

Chief Inspector Joseph Fox described the crime scene on the 2100 block of South Seventh Street as "very, very gruesome" and said the women had been stabbed multiple times.

Investigators this evening arrested a 21-year-old man from the neighborhood in the killings. Sambo Nou, of the 4000 block of Jackson Street, was charged with two counts of murder, robbery, and possession of an instrument of crime. He was awaiting arraignment this evening.

Police said Nou, whom they described as being the son of a friend of one of the victims, killed the women in an argument over money.

In the West Philadelphia killing, Appolonia Tucker was shot about 11:40 p.m. in a house on the 4900 block of Hoopes Street.

Fox, who called the teen's slaying "senseless," said investigators were interviewing witnesses. Police later issued an arrest warrant but declined to identify the suspect.

Fox said the fact that the killing grew out of something seemingly insignificant, however, did not set it apart from other homicides and was a "sign of the times."

Friends said Tucker made the trip to West Philadelphia from her home on the 1500 block of South 24th Street in Point Breeze to take the baby to visit the infant's father.

The investigation into the double slaying on South Seventh Street was complicated somewhat by a language barrier. The victims and the elderly woman who found them were Cambodian, police said.

The neighbor, who lives on the top floor of the three-story building, discovered the bodies when the women - one in her 40s, the other in her 50s - did not answer the bell when a van driver arrived to pick them up for work, officials said.

The woman found the door ajar and a bloody scene inside.

Outside today, residents watched from behind crime-scene tape as investigators went in and out of the building. The windows of the second-floor apartment had been opened and the curtains ruffled in a light breeze.

None on the street who were asked said they knew the women.

Lou Cinelli, who lives around the corner, said the neighborhood, where signs are in English and Cambodian, is troubled by drugs, prostitution and robberies, and he wondered what city officials were doing to stem the tide of crime.

"What's the plan?" he asked. "Are they going to make this area a red zone and be out here in force? They run wild around here."

On the Point Breeze street where Tucker lived, girls and young women erected a memorial of stuffed animals in front of her home.

"She was a sweet person and we all loved her," Markia Jones said.

Tucker was a 10th grader at Gratz High School. Her best friend, Ashia Hamilton, 14, said, "She was the light of the block, like the block fire."

Her godmother, Regina Thornton, lamented giving Tucker the SEPTA token for the trip to West Philadelphia.

The homicides occurred at a time when detectives are finding it harder to make arrests because of a reluctance of witnesses to come forward out of fear and a "no-snitch" culture.

Fox said one sign that things might be turning around is that police are getting more and more anonymous tips that sometimes lead to arrests.

Still, he said, when it comes to putting killers behind bars, "we need people to testify."

Contact staff writer Joseph Gambardello at 215-854-2153 or jgambardello@phillynews.com.