A trial involving a gay man charged with criminally exposing a sex partner to HIV began Tuesday in Johnson County district court in Iowa City. Aaron James Dahlberg, a Minnesota man, is charged with lying about his serostatus to an Iowa City man before they twice had unprotected sex on the night of March 31, 2000. Twelve state witnesses, including two other men who also say Dahlberg exposed them to HIV, law enforcement officers, and a doctor are scheduled to testify. The trial is expected to last two or three days. The Iowa law that makes it a felony to deliberately expose someone to HIV was enacted in 1998.