A judge unsealed documents Friday concerning a third murder charge against the man who is accused of killing his wife and mother-in-law.Michael Eugene Richardson, 57, was charged last year with the deaths of his 39-year-old wife Thao and 72-year-old mother-in- law, Than Lyi.The third murder charge stems from a missing persons case from 1992.According to prosecutor Enrique Camarena, Richardson was living in an apartment with 38-year-old Jovita Collazo and her 13-year-old daughter in National City when Collazo disappeared April 30. She was Richardsons live-in girlfriend at the time.The day after Collazo was last seen, both her daughter and estranged husband reported her missing to National City police, Camarena said.Richardson was a person of interest at the time of her disappearance; Collazo's body was never found, Camarena said.Camarena told 10News Richardson's arrest last summer triggered a second look at the Collazo case. "Already several people have come forward with information about Mrs. Collazo. The National City Police Department re-initiated its investigation into her disappearance in 1992," said Camarena.Olivia Richardson, who married Richardson in 1982, said she was in disbelief about the latest charges."I'm just too shocked," she said through her screen door.When asked if her former husband ever was violent with her, Olivia answered, "Not that I remember, no ... I don't remember."However, she said she does remember the heartache and shock she felt on the day he wanted a divorce."I [was] just married [for] two and half years," said Olivia. "Out of the blue, he just wanted a divorce. I don't know why ... I don't understand why."Richardson also is charged with carrying on a sexual relationship with his teenage niece.He was charged last summer with three counts of statutory rape, eight counts of oral copulation with a minor, and one each of rape with a foreign object and attempting to dissuade a witness stemming from the alleged abuse of his 17-year-old niece.At the time, authorities said Richardson was under investigation for the deaths of his wife and mother-in-law, who were found dead June 29 in a wrecked car off state Route 67 north of Lakeside.Investigators determined their injuries were not caused by a crash and called in homicide detectives.At Richardson's arraignment in July, Deputy District Attorney Chantal de Mauregne told a judge that Richardson escaped from a North Carolina prison in 1982 -- where he served time for robbery -- and remained on the lam for 18 years.Cab driver Ken Johnson, who was shot in the face by Richardson in that robbery more than three decades ago in North Carolina, told 10News Richardson should be locked away for good."But that messed my life up. I was two years trying to get over the wound. I'm 60 years old now and I'm still looking over my shoulder," Johnson told 10News from his Massachusetts home.The prosecutor said Richardson had assets of $10 million and had recently shuffled $500,000 between various bank accounts.The defendant's niece and her mother moved from Vietnam to Richardson's home in December, and the defendant quickly initiated a relationship with the girl that started with hugs and kisses and progressed to sexual activity in the first three months of 2010, the prosecutor alleged.De Mauregne said the defendant's wife discovered what was happening when she read text messages between the two.Richardson was arrested in March, but released without charges when the girl initially refused to cooperate.The teen told authorities "she was in love with the defendant, who said he would take care of her," the prosecutor said. "According to the victim, the defendant promised her he would leave his wife, be with the victim, and basically run off with her."District Attorney Bonnie Dumanis will decide after a May 24 preliminary hearing whether Richardson will face the death penalty or life in prison without parole if he's convicted.