According to articles linked from this one - there was also a lot of other evidence withheld:
* a strange van lurking in the neighborhood
* the wife's credit card turning up in a different city after the events
* dna evidence from semen in the bed
* dna evidence from a bloody bandana
(both things with dna point to the same person who wasn't morton)
And from the article you linked:
The investigator also received evidence that the attack was committed by a third party intruder -- a neighbor reported that she observed what appeared to be someone staking out the house and someone attempted to use the victim’s credit card in San Antonio. - See more at: http://www.innocenceproject.org/news-events-exonerations/pre...
That Anderson had all of that is enough to point to a reasonably strong suspicion of knowning, if not stricly knowing of Morton's innocence.
Here is the Innocence Project's original habeas petition: http://www.innocenceproject.org/files/imported/morton_writ_f.... It does not mention either the bandana nor the semen in its list (at 8-9) of evidence withheld by the prosecution in violation of Brady. The semen had been introduced at trial to support the prosecution's theory that Morton had masturbated over his wife's dead body (see 13). Morton requested a DNA test in 1990 that showed the semen was his.
Also note that the investigation and trial were in 1986-87. The first use of DNA testing in a criminal was in 1987, and testing would not be routine until many years later.
DNA testing which ultimately exonerated Morton wasn't available in the US in 1987; a single lab in the UK had pioneered the techniques but they weren't widely available. Arguably a bigger factor than the prosecutor's misconduct in Morton spending so long in jail is whatever procedural rule or individual prevented the DNA evidence from the bandana being brought up and tested until 2011. That was about 23 or so years too late.
The semen in the bed could instead actually have been a core part of the prosecution's crime of passion narrative if it had gone to trial: woman is killed in her own bed in act of brutal sexual violence a day after husband leaves her a note complaining about her unwillingness to have intercourse with him. Reports of unrecognised vans being parked in residential streets might be a police lead but are certainly not exculpatory evidence, and the credit card claims were apparently inaccurate (the police had her not-stolen credit card in their possession)[1].
Overall Anderson's actions are pretty consistent with someone certain he'd got the right man and willing to breach regulations to avoid him taking it to trial and getting off on the basis the evidence against him was as circumstantial as it was compelling. Misconduct which undoubtedly influenced Morton's plea, but it's still likely the judge would (reasonably) have ruled hearsay attributed to the accused's three year old son inadmissible and green vans irrelevant, leaving him highly likely to be convicted unless his defence team were able to successfully lobby for newfangled DNA fingerprinting techniques to be explored. There was, after all, a clear imputed motive consistent with the evidence, no sign of any break-in and no alternative suspects. Even conviction at trial might still have significantly improved Morton's chances of getting the bandana DNA raised at a much earlier appeal but one can't fix the failings of America's judicial system by levying probably unwarranted accusations of malice at one rule-bending prosecutor.
* a strange van lurking in the neighborhood
* the wife's credit card turning up in a different city after the events
* dna evidence from semen in the bed
* dna evidence from a bloody bandana
(both things with dna point to the same person who wasn't morton)
And from the article you linked:
The investigator also received evidence that the attack was committed by a third party intruder -- a neighbor reported that she observed what appeared to be someone staking out the house and someone attempted to use the victim’s credit card in San Antonio. - See more at: http://www.innocenceproject.org/news-events-exonerations/pre...
That Anderson had all of that is enough to point to a reasonably strong suspicion of knowning, if not stricly knowing of Morton's innocence.