HOLLYWOOD, Fla. -

Relatives of the four young men murdered in Hollywood this month believe the killings could be connected.

Jacob Rivera, one of the victims, was gunned down two days after his 16th birthday.

"He loved music and he loved girls," said Sara Crosthwaite, his mother.

Rivera was ambushed as he walked along Johnson Street in Hollywood on July 12.

"Just knowing we've lost Jacob forever, I don't even know to explain how I feel," Crosthwaithe said.

Surveillance cameras captured the gunman -- who covered his face with a white shirt -- as he ran up to Rivera, shot him in the head, then ran away. Friends told Local 10 that they believe the killing was gang-related. Hollywood police wouldn't confirm that or say if Rivera's murder is connected to three other killings in the city in just over a week, but relatives of the dead have begun connecting the dots.

"I'm just putting two and two together," said a man who asked Local 10 not to use his name but identified himself as the cousin of 20-year-old Donavin Johnson, who was shot to death four hours after Rivera was killed

Johnson was walking along South 28th Avenue near Jackson Street when he was shot. Police believe the shooter got away in a four-door white sedan with black molding on the side. Police have not released a motive for that killing. Family members said Johnson wasn't robbed.

Johnson's cousin told Local 10 that's he's not sure if Johnson knew Rivera, but he said the two men who were killed on Taylor Street last weekend were at his cousin's wake just hours before they were gunned down. Michael Baker and Andre Kemp, both 22, were shot to death in the early morning hours of July 20. Neighbors said the men were members of a local gang and often walked around with a red handkerchief hanging out of their back pockets.

"I mean, they were at the wake, and then the next day they get killed. I think they're related," Johnson’s cousin said.

He claimed Johnson wasn't in a gang but also didn't want to show his face on camera. Rivera's mother said her son wasn't affiliated with a gang either, but admitted she has moved out of her home for the safety of her family. Police reports and criminal records showed the four victims weren't strangers to violence or drugs.

Hollywood Police and the Broward Sheriff’s Office declined to talk about gang activity in South Broward County for this story.

Crosthwaite said she'll worry later about why her son was killed. Instead, she wanted to know who pulled the trigger.

"Even if you think it's stupid, just please tell someone what you know," she said.

Anyone with information on the four murders is asked to call Broward Crime Stoppers at 954-493-TIPS.