Biden Left 3 Fed Prisoners On Death Row. Why?

 Of the 40 on death row, Biden commuted the death penalty of 37.  I was curious why he left three to wait for execution.  

First, who were the three?  According to the NYTimes they were:

• Robert D Bowers, 52, convicted for gunning down 11 worshippers in the mass shooting at the Tree of Life Synagogue in Pittsburgh
• Dylann Roof, 30, who killed nine people at the Emanuel African Methodist Episcopal Church in Charleston.  
• Dzhokhar Tsarnaev, 31, who carried out the Boston Marathon bombing in 2013.

Bowers was also convicted of hate crimes as was Dylan Roof.  Tsarnaev, according to Wikipedia, was inspired by Al Qaeda.  

The people whose sentences were commuted  - taken off of death row, but left in prison without the possibility of parole - do not seem to have had an ideological motive.  

I didn't want to post this until I found some other source that identified a reason for why these three were different.  MSN.com quotes Biden himself.  

". . . Biden drew a firm line when it came to mass killings driven by hate or terror.  In his statement, Biden underscored his belief that while the death penalty should generally be abolished, exceptions must be made for 'cases of terrorism and hate-motivated mass murder.'

"These three men represent the kinds of crimes Biden deemed beyond the scope of clemency, crimes that not only claimed innocent lives but also targeted entire communities with terror and hatred. "  [emphasis added]

According to City View, the four people in the military on death row were not pardoned.

Of course, there are also bigger issues of our whole justice system which convicts a certain percent of innocent people every year,   From the Innocence Project:

"Extrapolating from the 281 known DNA exonerations in the US since the late 1980s, a conservative estimate is that 1 percent of the US prison population, approximately 20,000 people, are falsely convicted."

Then there are the differences in justice due to 

1. the ability of the wealthy to hire better lawyers, and the inherent racism in the US society as a whole which affects police, prosecutors, and judge.  
2. the economic and social causes of crime (huge gap between the rich an poor, poor education, poor access to physical and mental health care.  If these were addressed, fewer people would be led to crime by economic or social desperation.