AUSTIN — Long crime lab delays have forced at least 21 people across Texas to serve time on drug possession charges when the substance they had wasn’t illegal, according to a published report Sunday.The Austin American-Statesman found through interviews and by scrutinizing court records that 14 men and seven women pleaded guilty and began serving time before public lab results on the samples came back. Because of lab backups or delays, the test results didn’t arrive until months or sometimes years later. And prosecutors say there are almost certainly more of these cases, but no one is keeping close count. Many of the defendants involved are habitual offenders with long criminal history. Still, all the defendants identified by the newspaper were locked up for crimes of which they were later cleared. The false-positive drug tests date to 2005. But in just the last two years, 14 people wrongly convicted have earned belated exonerations. Tommy James Johnson is one. Johnson, 31, was confronted by Round Rock police in a Wal-Mart in June after he was recognized from security tapes showing him stealing a computer. Officers saw tracks on Johnson’s arms and found a backpack with syringes and a cotton ball soaked with a brown substance they believed to be heroin in his car. Johnson was charged with possession of less than a gram of the narcotic. After two months in the county jail, he pleaded guilty and was sentenced to six months in prison. He was released Dec. 11. The results came back from the Texas Department of Public Safety’s Austin crime lab in February, showing that tests on the cotton were negative. “We all — prosecutors, defense attorneys, judges, defendants — depend on rapid, competent forensic labs. But we have not had those in Texas for more than three decades,” said Patrick McCann, a Harris County public defender who represented Mario Martin in May 2008. Martin was charged with possession of 1.09 grams of cocaine but was exonerated after Houston’s crime lab returned negative results in February 2010. Those results came long after he was released. Thirteen of the cases identified by the newspaper were handled by the Houston Police Department’s crime lab. Inger Hampton, the assistant district attorney in charge of Harris County’s Conviction Review Section, said Houston’s lab carries an active caseload of about 2,500 drug cases – meaning that its first priority is “pending or active cases.” Eight of the identified cases involved forensic labs operated by the Department of Public Safety. DPS spokesman Tom Vinger said work at the agency’s 13 labs was slowed by a surge in blood-alcohol tests related to no-refusal operations and a shortage of lab technicians. At the end of 2012, the average processing time for drug tests was nine months. Last year, the Legislature authorized funding for 11 more lab technicians. Vigner said that, and a new policy limiting testing in misdemeanor cases, has brought the average wait for drug test results down to five months.