Two things can be true, the investigation was lacking and they are still able to prove their case.
One man says he was there that day during the specific time in question.
One man other people saw that day.
One man who admitted to (almost certainly) seeing the people who saw him.
One man who was admittedly dressed as BG.
One man whose car was caught on camera.
One man whose phone was suspiciously not caught up in the geofence despite his claims that he was using it.
One man admitted to drinking alcohol, going to the bridge, spotting the girls, following them, planning on raping them, getting disrupted,"cutting their necks," making sure they were dead, and covering them with sticks.
One man owned a .40 caliber handgun that matched the unspent cartridge found between the bodies.
One man confessed over and over.
One man said he stole a boxcutter from work, used it in the murders, and disposed of it in a CVS dumpster.
One man whose mental health declined after the murders.
One man who conveniently changed his timeline after he knew he was a suspect.
One man who ticks practically every box in regards to someone who has historically committed this type of crime (suicidal, substance abuse, depression, admittedly under the influence at the time of the crime).
They’ll never find a better suspect than that.