(Reuters) - A man arrested on suspicion of being involved in the killing of three homeless men and an attack on a fourth in San Diego was released from custody on Monday because of insufficient evidence he was connected to the crimes.

The suspect, identified as Anthony Alexander Padgett, 36, was arrested last Thursday in the suburb of Chula Vista.

"We discovered exculpatory evidence which does not give me confidence moving forward with Padgett still in custody," San Diego Police Captain Dave Nisleit told a news conference on Monday.

Padgett, described by Nisleit as homeless himself, told local broadcaster 10News at the time of his arrest that he was innocent.

Nisleit said he still believed the arrest was appropriate based on preliminary evidence as well as Padgett's conviction in 2010 for lighting another homeless person on fire. Nisleit said Padgett could again become a suspect in the case if additional information came to light.

The body of the first victim was discovered on fire on July 3 between a highway and train tracks in the Mission Bay area of San Diego, police said.

The following day before dawn, a 61-year-old homeless man was discovered bleeding, with trauma to his upper body, less than 4 miles south of the first attack, police said. He was taken to a hospital and remains in critical condition, Nisleit said.

Later that morning, another homeless man was discovered with severe wounds to his upper body and was pronounced dead at the scene near tennis courts in the Ocean Beach neighborhood.

Early last Wednesday, a homeless man was found critically wounded when he was set on fire outside a downtown San Diego apartment building, police said. That victim died of his injuries on Sunday, Nisleit said.

Police have said all four attacks appeared to have been the work of one person.

(Reporting by Curtis Skinner in San Francisco; Editing by Peter Cooney)