Trying to find the young thieves who visit town to enter unlocked vehicles overnight, — stealing from some of them and, when the keys are left inside, sometimes stealing the cars themselves — is like looking for a needle in a haystack for police, a Darien police captain recently told the Board of Selectmen. For the patrol officers on the night shift, there aren’t predictable places to look for the thieves, Marron said. “It’s all over town — it’s not just the borders, it’s not the dead-end roads. It’s just all over, so there’s no real prediction ability there,” Capt. Jeremiah Marron said. There are more reports of unlocked vehicles being entered in the warmer weather, he said.