LARGO — The letters turned up like clockwork.

Racist, vulgar, hate-filled threats that showed up in the mailbox of Amy Query, 25, and Nathan Maingi, 38, around every major holiday for the past two years.

The harassment prompted the interracial couple to change their routines. They stopped going for walks, neglected their garden. They installed security cameras, double-checked locks.

Still, the letters came.

"It was scary," Query said. "It never got easier without knowing who it was, always wondering, 'Is this person watching us?' "

The couple could finally put a face on their terror this week when Pinellas County sheriff's deputies arrested Allan Dale Richter, 56, a man who lived two blocks away in their Seminole neighborhood.

Richter targeted them, deputies said, because Maingi is black and Query is white.

"The letters were just probably some of the most disgusting things I've seen in my career in law enforcement," Detective John Spoor said at a news conference Tuesday afternoon.

Richter, who lived at 6339 Evergreen Ave, is accused of sending more than 20 letters between July 2010 and March. He was arrested Thursday in Missoula, Mont., where he moved last month to be "closer to people like him," Spoor said.

Richter is being held without bond in Montana until he can be extradited to Pinellas County, where he faces a charge of aggravated stalking and 18 counts of prohibition of generating acts with obscene, lewd materials. All charges have hate crimes attached to them.

If convicted, he could face up to 15 years in prison for stalking and up to 5 years apiece for the prohibition charges, according to Florida law.

The first letter the couple received was on July 4, 2010. It was written in black marker and taped to their door. It told Maingi to return to Africa — he is Kenyan — and suggested Query was a prostitute.

That was the last day their house felt like a home, Maingi said.

"In my opinion, someone who would walk up to your door and leave a note like that, what else could they do?" he said. "You just don't know."

The couple worried when Query learned she was pregnant in late 2010. The couple discussed moving, but decided against it.

They put cameras in the baby's room, knowing their child would embody everything their faceless assailant hated.

"The first thing that came to mind was, 'What if he sees me pregnant?' " Query said. "What if he sees the baby? It was a big deal."

In March, detectives had a break in the case when forensics picked up a partial fingerprint match on one of the letters. DNA evidence also was found. Both pointed to Richter, officials said.

"It was a huge relief that we know who it is now," Query said. "It's not every person that drives by, not every person who looks at us twice."

Richter has been convicted of carrying a concealed weapon, resisting arrest, brawling and disorderly conduct in the past, according to state records.

Times news researcher Carolyn Edds contributed to this report. Marissa Lang can be reached at mlang@tampabay.com or (813) 226-3386.