CHICAGO (CBS) — Aurora carpenter Greg Zanis has set up 58 wooden crosses in Las Vegas to honor the people killed in Sunday’s mass shooting.

White crosses bearing the names of those killed lined the Las Vegas Strip on Friday, in tribute to the people who died when a gunman opened fire on a country music concert from the 32nd floor of the nearby Mandalay Bay resort.

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The crosses will remain in place for 40 days.

“These are people that have lives, they have families that are now without them, and it just makes you appreciate the value of each moment,” one woman said in Las Vegas on Friday

Meantime, investigators continued trying to retrace 64-year-old Stephen Paddock’s steps in the days and months before the shooting, hoping to understand the motive for the massacre. Paddock killed 58 people and wounded hundreds more before taking his own life.

CBS News has learned the shooter’s longtime girlfriend, Marilou Danley, told the FBI she was concerned about his mental stability.

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Some security analysts have said they believe she knows more than she is revealing.

“She’s giving little pieces of information at a time. I think she’s really afraid to tell the truth. She’s not being forthright, because she’s afraid she may get into trouble,” CBS News law enforcement analyst Paul Viollis said.

Paddock picked Vegas for his attack, but he apparently had other possible targets in mind. He booked a room at a hotel overlooking Grant Park during Lollapalooza in Chicago, but never showed. He also researched hotels near Fenway Park, but there is no evidence he ever visited the city.

With that in mind, police planned to patrol the hillsides near the Rose Bowl on Friday while 60,000 music fans watch a Coldplay concert.

“We always worry about a copycat type of situation, no matter what incident occurs,” Pasadena Police Lt. Art Schute said.

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Security measures also were being finalized for outdoor events in Memphis and Austin, Texas, where fans have been offered refunds if they have safety concerns.