Patrick Eugene Johnson, the 60-year-old man accused in a string of rock-throwing attacks on I-35, is confessing in a series of jailhouse letters to KVUE News and the Austin American-Statesman.

Johnson does not say why he engaged in the attacks, which left an Austin musician with permanent brain damage, but said in the letters that he wishes to plead no contest to charges related to the rock-throwing cases.

He said he wrote the letters after a jury convicted him late last month on sexual assault with a child charges and was sentenced to 99 years behind bars. Johnson will be eligible for parole in 30 years.

The letters came about a month after Johnson wrote KVUE's Tony Plohetski that he didn't hit any cars with rocks and that he would grant an interview about the case. Johnson did not show up for subsequent scheduled interviews.

On Wednesday, Johnson's attorney told the Statesman that the letters were an emotional response to his recent prison sentence and that he will continue fighting the charges.

Austin police said they think Johnson is responsible for the vast majority of about 90 attacks during a two-year period that ended in June.

Austin police Cmdr. Steve Deaton said Wednesday that officers arrested a handful of copycats, including suspects with mental illnesses who were taken to psychiatric hospitals, and that about 10 to 20 cases remain open.

Those cases may have also been the work of copycats or could have been result of road debris.