By JO-MARIE BROWN and MONIQUE DEVEREUX
Criminologist Greg Newbold, of Canterbury University, said it was extremely common for prisoners to marry people who started writing to them while they were serving their sentences.
Arthur Allan Thomas - twice convicted of murder before being pardoned in 1979 - married a woman who corresponded with him in prison.
And in 1995, after serving a sentence for murder, Ross Appelgren married a juror from his original trial.
Dr Newbold: "In many cases they'll think the person is not guilty so they'll feel sorry for them and think they can help spiritually, emotionally and pragmatically to right the injustice."
The sociology professor said high-profile criminals often attracted the most attention, from women who thought they were exciting and mysterious.
"You get a situation where there is a lonely woman and a captive audience. She winds up getting a guy who she knows isn't going anywhere and who probably needs her. Women love to be needed."
One Paremoremo prison guard the Herald spoke to said it was quite common for inmates to marry people who wrote to them.
Watson, in particular, received lots of "sympathy mail".
"After a documentary screened on television about his case, he virtually needed his own mailbag."
Dr Newbold said having a spouse was very useful for a prisoner.
"They can run errands for you, write nice letters, support you at your parole board hearing and give you a kiss and a cuddle in the visiting room."
People became desperately romantic when they were in prison. "They often don't have any friends and no-one to give them the affection they might like.
"There's a lot of advantages for the inmate. The disadvantage for both parties is that neither of them really get to know each other properly."
Dr Newbold said that like any other relationships, some prison romances lasted and some didn't.
Zimbabwean refugee Shingirayi Nyarirangwe, 24, who is facing charges of infecting people with HIV, is planning to marry one of his victims in a prison ceremony in Auckland next month.
Wives are not obliged to give evidence against their husbands.
Ross Appelgren wed juror Julie Whittaker, who sent him letters in Paremoremo, eight years ago.
Yesterday Mrs Appelgren said the relationship was now very strong but she would never have married Appelgren while he was in jail.
She lost friends and was shunned by some family members because of her relationship.
She did not condone Appelgren's previous lifestyle, but she "saw a different side to him" and persevered because she felt it was right.
Speaking on National Radio she said that while the partner was in jail, "every moment is very, very precious, but there is no relationship.
That's when you form a bond, there can be no other relationship. You just talk and talk, share your innermost thoughts and feelings. Then you walk away and it's a week before you can go back."
Mrs Appelgren said Scott Watson's marriage surprised her.
"It can go nowhere and they've got another 10 years to wait for parole - it is a long time."
Others who formed long-term relations with women while in prison included Paul Bailey, in jail for the 1991 rape and murder of Otago schoolgirl Kylie Smith, and sex offender Stewart Murray Wilson, dubbed the Beast of Blenheim.
Prison romances in the United States are the subject of Sheila Isenberg's book, Women Who Love Men Who Kill.
Isenberg says it's all about women who are addicted to daytime TV soap operas and see prison dating as "Romance with a capital R".
The Howard League, an advocacy group for prisoner rights, supports marriage for inmates because it helps prisoners keep a sense of family and stability.
But New Zealand Relationship Services' clinical leader for the Auckland area, Louise Chapman, said inmates and women on the outside should beware of rose-tinted glasses.
"It's very similar to internet dating, in that the period of seeing only each other's best points goes on for much, much longer.
"When the real world stuff comes, it's quite a shock."
* Inmates can marry provided he or she is legally allowed to marry, is mentally competent, the marriage has been verified by the intended spouse; and "the marriage poses no threat to institution security or good order, or to the protection of the public".
* Inmates cannot give or receive gifts. Photos can be taken, but only one camera and one spare film are allowed. The ceremony must be "conducted without media publicity".
* Prisoners in New Zealand do not have conjugal rights.