By not sending a mission to Mars to explore sites where liquid water exists, NASA have made it very obvious that their priority is not to search for evidence of life on Mars. This is clear also by their attitude to potential FOSSILS that have been seen on the Martian images.
In 2004, Richard Hoagland raised the case that NASA's Opportunity Rover deliberately destroyed a potential fossil , an allegation subsequently supported by former NASA scientist Professor Richard Hoover in a video interview .
Geobiologist Nora Noffke was also certain she had identified microfossils in Gale crater, but Curiosity scientists Chris McKay and Ashwin Vasavada dismissed her evidence .
The wheel of the Curiosity Rover almost ran over another possible fossil discovered by Michael Ivey! 
When I saw this amazing picture, I went in search of a similar Earth fossil and found what's described as an "Uncurled Ammonite". I'm no palaeontologist, but I think the resemblance to this fossil was certainly worth NASA stopping the Rover to check it out. But once again they decided not to.
So we must ask: why does NASA tell the public they are spending billions to search for life on Mars, and yet when potential evidence for that life appears on their images, they just ignore it and command the Rover to keep going?
M J Craig
(1) Richard Hoagland article
(2) Prof. Richard Hoover video https://www.secretmars.com/videos-mars-et-ufos
(3) Nora Noffke article http://www.space.com/28218-mars-rover-curiosity-signs-life.html
(4) Possible fossil found by Michael Ivey, NASA original http://mars.jpl.nasa.gov/msl-raw-images/msss/00518/mhli/0518MH0261000000E1_DXXX.jpg