PORTLAND -- Reliable sources told KGW that investigators said there was probable cause to arrest Terri in connection with Kyron's disappearance, and for soliciting someone to kill her husband, but the choice has been for the investigation to continue.

So why not bring her in? Law enforcement experts said it's probably too soon. Probable cause is the minimum proof needed to make an arrest, explained former Multnomah County Sheriff's Capt. Bruce McCain. He said that's not enough to guarantee a conviction in the Horman case.

McCain said that before investigators make an arrest, they'd want proof beyond a reasonable doubt. McCain -who is also an attorney- said with only a minimum standard of proof met, it would make sense for prosecutors to wait for the highest level of proof before making an arrest.

The prosecution in this case is going to make sure that they have the strongest case possible before they drop that hammer, McCain said. One thing they don't want to do is to go in with a weak case that just meets the probable cause standard. That may not be able to lead to a conviction or a plea.

Investigators have been comparing where Terri said she was with what they have been able to establish about her movements that day. More: How Terri spent June 4

Meanwhile, the sources said that some of Terri's friends have not only been the subject of searches, they have been interviewed by investigators and, in some cases, took polygraph tests.

Terri has not been charged with any crimes, though law enforcement officials have made it clear she is the focus of the investigation.

But the key here is on the Kyron disappearance. Disappearing isn't a crime, said McCain. That's going to be a little trickier because what are they talking about? Are they talking about custodial interference, kidnapping conspiracy, solicitation a potential homicide without a victim? I don't think they're there yet.

McCain said the downside to waiting for an arrest would be if Terri were a flight risk or a risk to the public. He said it's obvious, at this point, detectives didn't think that was the case.

Complete coverage: Search for Kyron Horman

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