Just six days before alleged Grim Sleeper serial killer Lonnie Franklin Jr. is due in court for a hearing, Los Angeles police detectives are saying they have linked three additional murders and one attempted murder to the former South Los Angeles car mechanic.

The new cases raise the tally of potential victims to 16.

“Twenty-eight years is the span of Franklin’s criminal endeavor,” said LAPD Police Chief Charlie Beck, at a press conference Wednesday night at the Bethel AME Church in South Los Angeles. “We may never know how many young women Lonnie Franklin killed.”

The new victims, who range in age from 22 to 43, were linked to 59-year-old Franklin through MO, ballistics, and DNA evidence. Los Angeles detectives discovered the additional slayings after combing through hundreds of unsolved homicide cases and missing-person reports dating back to May 1976, when Franklin returned from military service in Germany.

Franklin allegedly is one of five known serial killers who roamed the streets of South Los Angeles during the crack epidemic of the 1980s. He was arrested at his home in July 2010, after investigators found that DNA evidence taken from a slice of pizza he had been eating positively matched DNA taken from semen and saliva found on his victims. Franklin was tracked down through familial DNA testing after his son, then 28, was arrested on a weapons charge in the summer of 2009, and had to give up a DNA swab.

Franklin already is charged with the murders of 10 women and the attempted murder of another. Most of his alleged victims, who ranged in age from 14 to 35 years old, were shot with a .25-caliber pistol. Others were strangled. Their bodies were discovered between 1985 and 2007 under filthy rugs and mattresses in dumpsters and alleyways along a sleazy stretch of Western Avenue in South Los Angeles known for cheap motels, liquor stores, and storefront churches.

At the press conference, police identified two of the new victims as Sharon Dismuke and Georgia Mae Thomas. Dismuke was discovered shot in the chest in the restroom of an abandoned gas station in January 1984. Thomas, who was 43, was found on a sidewalk in the 1800 block of 57^th Street, just a block away from where Franklin’s mother-in-law owned a house, in December 2000. She had been shot twice in the upper torso with a small-caliber pistol.

Police said the weapons used to kill the two women were found inside Franklin’s home during a three-day search. The gun used to kill Dismuke also was used in the alleged slaying of Franklin’s last known victim, 25-year-old Janecia Peters. Peters’s body was found in a dumpster by a homeless man on Jan. 1, 2007.

The third victim, Regina Theresa Beaty, was found dead in an alley in August 1992. Like the other victims, she was shot in the upper torso with a small-caliber pistol.

Police also believe Franklin attempted to kill a 22-year-old woman in May 1985. The survivor told police that Franklin picked her up, shot her in the chest, then sexually assaulted her, before pushing her out of his car. He was “persistent in picking her up,” said a law-enforcement source. The source said the incident was eerily similar to the attack on Enietra Washington, the only other known surviving victim.

“It goes to show you that we are dealing with a terrible person who has no regard for human life,” said Porter Alexander, the father of 17-year-old Monique Alexander, one of Franklin’s alleged victims.

Police have long thought that Franklin was involved in additional slayings. Last April, police linked him to the alleged murders of three more victims. Two of the women disappeared in 2005, and their photos and identification were discovered in an envelope hidden inside Franklin’s freezer in his garage. Their bodies have never been found.

“We have concluded that we are now considering them homicide victims,” said LAPD detective Dennis Kilcoyne. “If they walked through the door we would be happy, but I don’t think so.”

Both women were last seen in the vicinity of Franklin’s home at 81^st and Western Avenues. The identities of the two women came to light in July 2010, when detectives seized hundreds of photos and videotapes from Franklin’s home. Some of the pictures, which were taken by Franklin, showed women who ranged in age from teenagers to their 60s, exposing their breasts or fully nude.

The third victim identified last April was Inez Warren. Los Angeles County Sheriff’s deputies discovered her body in an alleyway off Western Avenue on Aug. 15, 1988. She had been shot once in the chest. An anonymous person called in to report her murder. Police said they have since matched the caller’s voice to Franklin.

Police are not ruling out that Franklin may be responsible for even more slayings. Kilcoyne said the Los Angeles Coroner’s Office has at least 90 Jane Doe cases that have not been solved, and hundreds of missing-persons cases.

Franklin, a pensioner who collected $1,658 monthly from the city, had been living in the epicenter of the killings since the early ‘80s, when he was working as a trash collector for the city’s Department of Sanitation. Many of the Grim Sleeper killings occurred during the same years Franklin claimed he was injured on duty.

Police do not plan to charge Franklin in the additional killings, because that would slow progress toward a trial. A pretrial hearing for Franklin is scheduled for Monday.