After seven years' flight across half the globe, David Davis' luck ran out. The man accused of killing his young wife, Shannon, on their southern Michigan farm in 1980 has been arrested in American Samoa in the South Pacific.

A television show was Davis' downfall. The FBI and local police in the capital, Pago Pago, arrested Davis on Friday after a tip from a viewer of NBC-TV's Unsolved Mysteries.

The case twice was featured on the show because it combined mystery, deception, and more than $300,000 in insurance money, and because Davis appeared to have dropped off the face of the Earth after 1981.

Davis, 44, a former University of Michigan graduate student in pharmacology, is accused of injecting his wife of 10 months with a muscle relaxant that killed her, and then masking the deed by bashing her head on a rock and telling police she fell off a horse.

Hillsdale County authorities believed him and ruled the death an accident, but a tenacious state cop, detective Sgt. Don Brooks, believed otherwise. After a 14-month investigation, the state Attorney General's Office took Brooks' evidence before a grand jury that returned a first-degree murder warrant.

Police came close to capturing Davis in Port au Prince, Haiti, on Christmas in 1981, but he fled, leaving behind his sailboat.

''It has been eight years of hell,'' said Shannon Davis' mother, Lucille Mohr of Toledo, Ohio, after police notified her and her husband, Robert, of their son-in-law's arrest. ''My heart is coming out of my chest,'' she said. ''I wanted him so bad.''

Shannon Mohr was 25, still living at home with her parents, when she met David Davis at a wedding party in Sylvania, Ohio, Aug. 4, 1979. She had attended Catholic schools in Toledo, where she grew up, attended nursing school and became a registered nurse.

Her pay from a Toledo hospital was the only money coming into the Davis household after she married David in Las Vegas just eight weeks after they met.

A Detroit Free Press investigation showed that David Davis bought a $220,000 insurance policy two days after returning from their honeymoon, naming himself as beneficiary if Shannon died.

Within a short time he was beneficiary to five other policies. In all, he stood to collect more than $300,000 if she died.

The following summer, she did, on July 23, 1980, in a wooded area of their farm outside Pittsford, 100 miles southwest of Detroit.

Shannon's parents became suspicious at the hospital where their daughter was dead on arrival. The Mohrs said later that Davis told them Shannon wanted to be cremated, against their Roman Catholic faith and what they understood to be their daughter's wishes.

Also suspicious was a neighbor, farmer Richard Britton, who wrote to the Michigan Attorney General's Office that things weren't exactly right.

''I never thought they would catch him,'' Britton said Friday after he learned of Davis' arrest in American Samoa, a U.S. territory in the South Pacific halfway between Hawaii and New Zealand.

The FBI and police arrested Davis at Tafuna International Airport, where he was working in an office job for Pacific Island Airways. He had been living under the name David Myer Bell.

NBC spokesman Charles Barrett said a female viewer called the show's toll-free number after watching the Dec. 28 broadcast in the United States. He said she knew Davis from visits to American Samoa, and she provided authorities with information that led to the arrest.

Davis, 44, collected on two small insurance policies after his wife's death but fled without collecting on the rest of the $300,000.

Since his disappearance, Davis has lived in Florida, the Caribbean, Alaska and Hawaii, in addition to American Samoa, officials said.

Davis apparently has been living in American Samoa since 1985 and had married a Samoan woman, Maria Koleti Sua.

The couple lived in the village of Tafuna, about eight miles from Pago Pago and near the airport.

The FBI is flying Davis to Hawaii to start extradition proceedings to return him to Michigan.

Shannon Lou Mohr Davis