Story highlights California man was standing near a mailbox at the Boston Marathon finish line

While cheering for his wife, second bomb explodes, sending debris flying

Mailbox survives the blast, and he survives with puncture wounds to legs

Darrel Folkert of Redondo Beach, California, stood next to a mailbox near the finish line of the Boston Marathon to cheer on his wife as she completed the race.

Moments later he was suddenly thrown by a loud explosion that shattered windows behind him, lifted tables from their foundations and tossed chairs along the sidewalk.

"He was standing right next to the mailbox when it exploded," his wife, Jac Bost, told CNN in a phone interview.

The mailbox, one of the only objects left intact after the second explosion and the site where authorities have focused their investigation, may have saved Folkert's life. He suffered non-life-threatening puncture wounds to the leg and returned last week to Los Angeles, where he is recovering, Bost said.

Folkert and Bost, both 42, are avid ultra-marathon runners, competing in events with distances of up to 50 miles.

Photos: Boston bombings: The week in photos Photos: Boston bombings: The week in photos The second of two explosions goes off near the finish line of the Boston Marathon on April 15, 2013. Three people were killed and at least 264 were injured in the double bombings. Hide Caption 1 of 23 Photos: Boston bombings: The week in photos A man comforts a victim at the scene of the first explosion. Hide Caption 2 of 23 Photos: Boston bombings: The week in photos Runners react near Kenmore Square after the explosions. Hide Caption 3 of 23 Photos: Boston bombings: The week in photos Rescue workers tend to the wounded on the scene. First responders tried to save lives and limbs before transporting victims to hospitals. Hide Caption 4 of 23 Photos: Boston bombings: The week in photos On April 16, 2013, a vigil was held at Boston's Garvey Park for 8-year-old bombing victim Martin Richard . The other victims were Krystle Campbell , a 29-year-old restaurant manager from Medford, Massachusetts, and Lingzi Lu , a 23-year-old Chinese national attending graduate school at Boston University. Hide Caption 5 of 23 Photos: Boston bombings: The week in photos The city was quiet the day after the tragedy. Here, a young runner, left, sits in a church near the scene of the attack. Hide Caption 6 of 23 Photos: Boston bombings: The week in photos On April 17, 2013, a federal law enforcement source with firsthand knowledge of the investigation told CNN that a lid to a pressure cooker -- thought to have been used in the bombings -- had been found on a roof of a building near the scene. It was one of several pieces of evidence authorities found Hide Caption 7 of 23 Photos: Boston bombings: The week in photos The device also had fragments such as nails, BBs and ball bearings, the FBI said. Hide Caption 8 of 23 Photos: Boston bombings: The week in photos On April 18, 2013, the FBI released photos and video of two suspects in the bombings and asked for the public's help in identifying them. Hide Caption 9 of 23 Photos: Boston bombings: The week in photos The FBI later identified the suspects as Dzhokhar Tsarnaev , left, and his brother Tamerlan Tsarnaev Hide Caption 10 of 23 Photos: Boston bombings: The week in photos FBI Suspect No. 2, later said to be Dzhokhar Tsarnaev, is apparently seen in this picture, far left in white cap. The photo was taken by Boston Marathon runner David Green at the scene of the bombings. Hide Caption 11 of 23 Photos: Boston bombings: The week in photos The man identified as Dzhokhar Tsarnaev appears in a tighter crop of Green's photo. Green submitted the photo to the FBI, he told CNN's Piers Morgan in an interview. Hide Caption 12 of 23 Photos: Boston bombings: The week in photos Late on the night of April 18, 2013, police responded to a call that a campus officer at the Massachusetts Institute of Technology was shot and killed. Police said a man later reported being carjacked by the brothers. The two were stopped in Watertown, Massachusetts, where police said they threw explosives and shot at the officers. One man, assumed to be Dzhokhar Tsarnaev, drove off. The other, later identified as Tamerlan Tsarnaev, was injured. He died at the hospital. Hide Caption 13 of 23 Photos: Boston bombings: The week in photos Boston Police Commissioner Edward Davis speaks to the media on April 19, 2013, and explains that the city is on lockdown until the surviving suspect is found. Hide Caption 14 of 23 Photos: Boston bombings: The week in photos Officers scoured Watertown, Massachusetts, where Dzhokhar Tsarnaev was last seen. Hide Caption 15 of 23 Photos: Boston bombings: The week in photos Frightened residents were questioned near Dzhokhar Tsarnaev's home in Cambridge, Massachusetts. Hide Caption 16 of 23 Photos: Boston bombings: The week in photos SWAT teams conducted door-to-door searches in Watertown while looking for the suspect. Hide Caption 17 of 23 Photos: Boston bombings: The week in photos Ruslan Tsarni , uncle of the Tsarnaev brothers, gave an interview April 19, 2013, outside his home in Montgomery Village, Maryland. He urged Tsarnaev to turn himself in. Hide Caption 18 of 23 Photos: Boston bombings: The week in photos SWAT teams continue to search in Watertown on April 19, 2013. Hide Caption 19 of 23 Photos: Boston bombings: The week in photos On the evening of April 19, 2013, a Watertown resident called the police and reported seeing a man on a boat in his backyard. Residents ran from the area where police said Dzhokhar Tsarnaev was hiding on Franklin Street. Hide Caption 20 of 23 Photos: Boston bombings: The week in photos Helicopters with infrared devices detected a man under the boat tarp. Dzhokhar Tsarnaev's frame is seen in this thermal image released by Massachusetts State Police. Hide Caption 21 of 23 Photos: Boston bombings: The week in photos Police threw "flash-bangs" -- devices meant to stun people with a loud noise -- and started negotiations with Tsarnaev. He eventually surrendered and was transported to a local hospital in serious condition. Hide Caption 22 of 23 Photos: Boston bombings: The week in photos People wave U.S. flags in Watertown after it was announced that Tsarnaev had been captured. Hide Caption 23 of 23

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Bost, a marketing executive, was competing in her seventh Boston Marathon and was less than a quarter mile away from the finish line when she heard a loud boom. She said organizers stopped her as word spread of an explosion and people began frantically running away from the scene.

At first, she did not know what had happened to her husband, but strangers lent her a phone so she could contact him.

Meanwhile, two men carried an injured Folkert to a nearby store, where they called 911 and lent him a phone to call relatives, she said.

"It was the extreme generosity of people of Boston who offered to help that deserve the praise in the aftermath of what happened," she said.

Folkert, who is expected to fully recover, and Bost are hoping to locate the two men who treated him at the scene and the others who helped them reunite, Bost said.

"Everyone in the city of Boston was phenomenal, and I can't understate the level of generosity we received," she said.