Westminster Police say it happened around 2:50 a.m. outside the King Soopers at 103rd and Federal.

They say the tall, heavy-set man, later identified as 26-year-old Ryan Patrick Nichols, was loitering in the parking lot prior to the assault.

Police say when the 80-year-old man, identified by his family as Dean Withers, walked by Nichols, right at the front doors of the King Soopers, Nichols stabbed Withers once in the back.

According to police, the stabbing appeared to be totally random and unprovoked.

"There really wasn't a reason that we can discern at this point. It appears to be just a senseless random act of violence. I don't think there was an exchange of words or anything else between the two," said Investigator Wayne Read with the Westminster Police Department.

Withers' daughter-in-law, Jill, says he was arriving at work when he was attacked.

"He's probably one of the most caring, helpful individuals that I know. He would give the shirt off of his back to a complete stranger to help them out," Jill Withers said. "Most of his repeat customers at his store know him personally."

Police say Nichols was caught around 7:30 p.m. on Monday after an anonymous tip led them to the 3000 block of West 107th Place in the Autumn Chase Townhome subdivision.

Nichols was seen in the King Soopers parking lot over the previous two nights as well, according to police. He faces charges of first-degree assault and crimes against at-risk adults. Nichols has a lengthy criminal record.

"We're ecstatic. We were hoping for a good outcome before the end of the day so we could go home and everybody could rest easy," Jill Withers said. "Everybody's a little bit relieved, because we know now that the person who attacked, or potentially attacked him is in custody and it's not going to happen to somebody else."

Withers' family says he is recovering. Jill Withers says he spent the weekend with his grandchildren, spending a day at Water World and a day at Elitches.

"[I'm] just in shock that someone would do this, especially to an 80-year-old man, to anybody," she said. "[We want to see] that he's brought to justice so someone else's husband, or grandfather, or father, won't be in this position."

"We've got questions, we want to know why. You know, whenever anybody is assaulted you want to know why. What were they thinking? Hopefully we'll get some answers," Jill Withers said.

A spokesperson for the hospital says Withers is in serious condition but is doing well and is expected to be moved to a regular hospital floor sometime Tuesday.