A former Minneapolis school teacher who pleaded guilty to trading messages about sex with a police investigator posing as a 14-year-old girl had a history of swearing at his students.

Joel D. Fowler, 23, of St. Louis Park, was reprimanded in February for his behavior and warned that if he didn't change, he could face further discipline and possible firing. When Fowler was charged May 29 in Ramsey County District Court in the undercover sex sting, the school district said that he had no history of complaints.

But personnel data the district released this week show that he did have complaints on his record, and that school officials were concerned about his behavior. He told a student to "get the [expletive] out of my room," said a Feb. 7 letter written by Evelyn Kimble, assistant principal at Olson Middle School.

Fowler was a seventh-grade social studies teacher at Olson Middle School. His employment was terminated on June 27.

"As you know, [Principal Karon Cunningham] and I discussed early on in the school year the need to be professional at all time with students," Kimble wrote in the letter addressed to Fowler. "At that time you used inappropriate language with students. It is unfortunate that this is the second occurrence in which you used inappropriate language with a student."

Kimble's letter did not elaborate on the previous incident. She urged Fowler to "stop, think, act responsibly."

"When you feel your control is slipping away, your first instinct is to talk louder and faster, you show you are nervous, scared and out of control," she wrote.

Fowler was arrested after he posted an online ad on Craigslist looking for sex with high schoolers that was discovered by St. Paul police. Fowler told a sergeant posing as a girl that his name was "Blake," and arranged to meet with her at Cherokee Park in St. Paul, where he was arrested as part of the undercover sting, Operation Broken Heart.

Fowler was charged with one count of engaging in electronic communication relating to or describing sexual conduct with a child, and soliciting a child through electronic communication to engage in sexual conduct. He pleaded guilty on June 26 to the first count and is scheduled to be sentenced on August 22.

Fowler was first hired as a temporary employee with the district in August 2011, and was hired fulltime at Olson Middle School in August 2013, earning a salary of $46,663.

By Chao Xiong