The doctor killed in a mass shooting by former NFL player Phillip Adams wrote books about experiencing God and 'angels' in the ER where he worked.

Dr Robert D Lesslie, 70, was killed alongside his wife of 40 years Barbara, and their two grandchildren, Adah Lesslie, 9, and Noah Lesslie, 5. 

Also killed in the shooting at the Lesslies' family home in South Carolina last Wednesday were air conditioning technicians James Lewis and Robert Shook, both 38. 

Adams took his own life the following day as police closed in. 

Dr Lesslie was the author of a number of books about faith.

Describing the meaning he found in his work, he said in his bio: "I enjoy the fast-paced environment of the ER and the need to make rapid and accurate diagnoses.

"I view my medical career as an opportunity to go beyond simply diagnosing and treating individual patients. For me, it is a way to fulfill a higher calling by meeting the real physical and emotional needs of patients."

In Angels in the ER, he wrote about the everyday 'angels' he encountered at work in the form of friends, nurses, doctors, patients and strangers who offered help in the midst of trouble. 

His follow-up book, Angels in the ER Volume 2, was due to be released this August. 

Police have not yet confirmed a motive for the shooting but Adams' father was one of Dr Lesslie's patients. 

Adams was in the NFL for six years, playing for the San Francisco 49ers, New England Patriots, Seattle Seahawks, Oakland Raiders, New York Jets and the Atlanta Falcons.

York County Sheriff Kevin Tolson told reporters that the hearts of Dr Lesslie's loved ones "are bent toward forgiveness and peace", and that they are also praying for Adams' family.