UPDATED 04/26/11 6:29 p.m.

ROUND LAKE PARK, Ill. (CBS) — Drugs and alcohol are believed to be involved in the death of a mother from Round Lake Park, who had been missing for 10 days until her body was found.

The body of Melissa Ann Best, 34, was found in the back of her minivan Monday evening in the parking lot of a Grayslake parking lot.

“This has been a long and intense investigation going over the course of approximately a week and a half, with little or no information as to her whereabouts,” Round Lake Park police Chief George Filenko said.

LISTEN: Newsradio 780’s Mike Krauser Reports

Best had last been seen driving her Pontiac minivan on April 15, after she dropped off her teenage daughter at a friend’s house in a neighboring suburb. Police believe that was the last day of her life, Filenko said.

The investigation so far indicates that Best drove to a location in Waukegan, where something happened that led to her death. She was then driven to the parking lot of the Grays Point Studios apartment complex, near Routes 120 and 45 in Grayslake.

The parked van was found around 6:50 p.m. Monday evening, based on tips police received through Facebook.

Best’s body was reclining in the back seat of the van.

Lake County Coroner Artis Yancey said Tuesday there were no outward signs of trauma on her body and that an autopsy is scheduled for 1:30 p.m. Wednesday.

Filenko said Best knew the people she went to meet in Waukegan, and there are persons of interest who could be charged with concealing her death.

Drugs and alcohol are believed to be involved in Best’s death, Filenko said. She had a history of alcohol abuse, and tested positive for opiates, he said.

But as to the specific cause of death or what kind of drugs she took, Filenko said, “At this point, there’s nothing conclusive until we get the autopsy results back.”

Reports that Best was strangled are not correct, Filenko said.

Best did not have a cell phone or credit card on the day she was last seen, but other personal belongings were with her in the van, Filenko said.

Filenko said previously that Melissa Best’s husband, Clint Best, is not a suspect. He told WBBM Newsradio 780’s Mike Krauser that Clint Best has been cooperating with police.

Filenko visited Clint Best last night to inform him about the discovery of his wife’s body. The police chief described Mr. Best as “devastated” by the news.

Filenko and Clint Best have said it would be highly unusual for Melissa Best to just take off. She had cash when she disappeared, but it is not known how much.

Earlier, Filenko described Best as a “homebody” who “lived a relatively non-social lifestyle.”

The Sun-Times Media Wire contributed to this report.

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