A 25-year-old Saginaw man who pleaded guilty to aggravated sexual assault of a child and online solicitation of a child was assessed sentences of life and twenty years in prison in a punishment trial that concluded late Wednesday in a Weatherford district court.In April, Johnathan Eugene Cooper pleaded guilty to the October 2008 charges and elected to have Parker County District Judge Trey Loftin assess his punishment, a news release from the Parker County district attorney's office said.During the course of the trial, five different women testified that they had sex with Cooper when they were between 13 and 16 years old and he was an adult. One woman also said that he told her that he had previously had sex with an 11-year-old.Three other women testified that after they had sex with Cooper, he asked them to arrange for him to have sex with underage girls."Sir, you are a serial child rapist," Loftin said in sentencing Cooper. "You're obsessed with young girls."The defendant had been free on bond in a Tarrant County sexual assault case at the time of the Parker County offense, Parker County Assistant District Attorney Jeff Swain said in the news release. After the Parker County offense, when he posted bond again, judges in both counties required Cooper to be on an electronic monitor, Swain said."One of the most offensive things that came out during the trial was a text message that this defendant sent to our then-13-year-old victim in which he asked her to arrange for him to have sex with a 6-year-old girl," Nikki Morton, the prosecutor who tried the case with Swain, said in the news release.While on the electronic monitor, he committed the Johnson County offense with a teenager whom he met online, which is the same way he met the victim in the Parker County case, Swain said."The fact that he would not change his behavior despite being on bond and having his whereabouts continually monitored showed that he would not stop until he is forced to do so," Swain said in the news release.Officers who testified about the Johnson County offense said that when they executed a search warrant on Cooper's house, they found a stack of papers related to the Parker County offense, including several photographs of cellphone screens containing what appeared to be blackmail messages sent to him from the Parker County victim.However, Cooper's ex-girlfriend testified that Cooper used computer software to create the texts and send them to a cellphone so that they would appear to be sent to him from the victim when, in fact, they were fabricated. She also said that Cooper ordered a fake driver's license from California for the victim which showed her to be over 21 years old in an attempt to manufacture a defense.Prosecutors also introduced evidence that, despite bond conditions prohibiting him from contacting the victim, Cooper created an alternative MySpace account and continued to contact the 13-year-old girl in an attempt to create a defense."This was one of the most devious and manipulative defendants that I have prosecuted," Morton said in the news release. "With all of the victims that he has had over the years and since he committed two sex offenses while on bond for another sex offense, he deserved a lengthy prison sentence."Cooper still faces sexual assault charges in both Tarrant and Johnson counties, the news release said. He will be eligible for parole on the Parker County sentences in 2040.