JEFFERSON CITY, Mo. (AP) — Missouri prosecutors could use evidence of past criminal behavior in child sex abuse prosecutions under a measure given preliminary approval Wednesday by the state House.

The proposed state constitutional amendment would allow use of relevant evidence of past criminal acts to corroborate a victim's testimony or to demonstrate the defendant has a propensity to commit the crime with which he or she now is charged. That type of evidence would be limited to prosecutions of crimes with a sexual nature in which the victim was younger than 16.

Rep. John McCaherty said federal courts and many states already allow for such evidence. He said child sex abuse cases are unique.

"We need to do everything we can to protect our children from sexual predators," said McCaherty, R-High Ridge.

A state task force created in 2011 to focus on preventing child sex abuse in Missouri recommended among other things that the Legislature pass a constitutional amendment allowing for such evidence. In a January report, the task force said frequently there's no physical evidence in sex abuse cases and that perpetrators say they have no memory of sexual contact. In those instances, it becomes the child's word against the adult's, which makes it harder to prove guilt.

House members gave the constitutional amendment first-round approval by voice vote. The measure needs second-round approval before moving to the Senate. The proposal would require voter approval if it passes the Legislature.

A constitutional amendment is required because the Missouri Supreme Court previously has struck down a state law allowing prior sex offenses to be used against defendants facing similar new charges. A unanimous court ruled in December 2007 that using evidence of previous crimes to prove a defendant's propensity to commit a crime "violates one of the constitutional protections vital to the integrity of our criminal justice system."

Missouri's original 1994 law that dealt with such evidence was struck down by the high court in 1998. That prompted lawmakers to pass a revised version two years later, which was rejected in 2007.

The statute says that for sexually oriented criminal charges involving a victim younger than 14, the courts can admit evidence that the defendant has committed other sexual crimes involving children younger than 14 to show "the propensity of the defendant to commit the crime" unless "the trial court finds that the probative value of such evidence is outweighed by the prejudicial effect."