(AP Photo/The Birmingham News, Jeff Roberts)

BIRMINGHAM, Ala. - Police investigating a possible robbery at an Alabama home early Sunday instead found five people dead inside, authorities said.

Birmingham Police Sgt. Johnny Williams said officers arrived at the house around 3:30 a.m. Sunday after getting a call that a robbery was in progress and soon discovered the five victims. He told reporters that investigators are interviewing potential witnesses but so far have made no arrests.

The victims' identities and the causes of death were not immediately released. Birmingham authorities launched a homicide investigation and police believe more than one person was involved.

"It obviously appears to us this horrific crime was not a random act of violence," said Birmingham Police Chief A.C. Roper.

The two-bedroom house, which is made partly of cinderblocks, was built along a busy street in west Birmingham. Vacant homes sit beside houses where some residents have lived for years. One is Beatrice Houston, who lives across the street from the home where the bodies were found.

Houston, who is 64, said she believes a woman, her son and her brother had lived in the house for the last year or so. She said she didn't know the neighbours' names, but started worrying when she saw groups of young men hanging around the house at odd hours.