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PLEASANTON, Calif. - The search for a missing runner in the Pleasanton hills enters a new phase Wednesday.
Philip Kreycik, 37, has not been found after four days of exhaustive searching.
Authorities say they are scaling back into a "limited objective" mode.
"I can tell you in my career this is an unprecedented search in Alameda County," said Ron Seitz, head of Search and Rescue for Alameda County.
Seitz has spent 45 years locating missing persons, and says most are found within 24 to 30 hours.
In Kreycik's case, the strategy now will be to review and re-evaluate.
"We'll look for gaps in our coverage patterns and make sure there are no holes or any areas of significance we may have missed," said Seitz.
Tuesday was the biggest day of searching yet: more than 120 trained searchers, volunteer teams from all over California.
"I don't think you could be up on a ridge today and not heard someone yelling, 'Philip, Philip, hello, are you there?'", said Sgt. Ray Kelly of the Alameda County Sheriff's Dept.
"And they are finding lots of things, watches, sunglasses, we actually found some blood on a rock that we sent to the crime lab, where it was determined to be animal blood."
Kreycik, an avid trail runner, planned and mapped his intended route in the Pleasant Ridge Regional Park.
It was an 8 mile loop, defined trails and a fire road, nothing tricky.
But that area was scoured first, expanding into a 16-square mile search area, and still no trace of Kreycik.
"Philip is a marathon runner, he loved to run and was very systematic in how he did that sport," noted Kelly.
Kreycik's SUV, parked at a trailhead, had his wallet, phone, and shirt in it.
Wearing just shorts and shoes in 104 degree heat, he set off.
Search dogs found but lost his scent after a short distance; it's believed to have been eroded by heat and wind.
But in a park that has hundreds of visitors daily, not one person has said they saw Kreycik running at midday Saturday.
"We have two possible scenarios at this point," said Lt. Erik Silacci, head of investigations for the Pleasanton Police Dept.
"One is Philip is somewhere up there in the mountains, and number two, he parked his vehicle and he is somewhere else."
Kreycik is a scientist, married with two children, with no history of instability.
His disappearance has motivated dozens of volunteers to flock to the hills to search on their own.
Many are organized by leaders of a "Find Philip Kreycik" Facebook page.
""We'll keep coming out here, it costs us nothing, we come out here anyway," said mountain biker Benny Suarez, riding near the Santos Ranch Road trail, which was part of Kreycik's intended route.
Suarez and fellow rider Eduardo Zavala said they logged 16 miles Tuesday, looking for him, and would be returning Wednesday.
"If I have a choice of going the regular way I normally ride, or going a different way on the off-chance I might find him, that's what I'm going to do," said Suarez.
The Sheriff's Department has spent each night flying the hills with heat-seeking night vision, so sensitive it shows rocks still hot from the daytime sun.
"We're able to pinpoint small animals down on the ground, that's the level of detail we're seeing," said Kelly.
"But we're having a hard time at this point saying we can locate Philip at all."
Searchers have also found deer and sheep carcasses, the remains of mountain lion attacks, although attacks on humans in the park are rare.
With so few answers, authorities are now asking anyone who saw Kreycik at any time or place on Saturday to contact them.
"He's either incapacitated in the search zone, and we can't find him, or he's not here and he's somewhere else," said Kelly.