Victorville , California ( CNN ) -- Mike McStay has come to this remote swath of Southern California desert to say goodbye . To his brother , Joseph McStay . His sister-in-law , Summer . His two nephews , 4-year-old Gianni and 3-year-old Joseph Jr. All four ended up here , in an unincorporated area north of Victorville , in a pair of shallow graves , for reasons no one has been able to explain . There 's no bringing them back . But Mike McStay promises they will get justice , once their killers are found . `` You guys are cowards , '' he said . `` And all of America is coming after you . And we 're going to find you . And we 're going to prosecute you . '' If and when authorities track the person or people responsible down , as they 're taken through the criminal justice system , they will have company . Mike McStay vows : `` I 'm going to be there every step of the way . And I 'm going to be there when you meet your fate . '' So who are the culprits ? Why did they kill the McStays ? And how did they end up here -- the husband and wife in one grave , their two sons in the other -- their bones visible in the dirt to a motorcycle rider going through ? All good questions without answers , officially at least . In February 2010 , the McStays had a busy but seemingly happy life in Fallbrook , a community of about 30,000 people about 18 miles from the Pacific Coast and 50 miles north of San Diego . In addition to chasing after their two little boys , Joseph and Summer -- who married three years earlier -- were remodeling their home . `` They were happy , '' Mike McStay told HLN 's Nancy Grace earlier this month . `` And that 's part of the mystery . '' The last documented sighting of them was February 4 , 2010 . The family 's locked , abandoned Isuzu Trooper was located four days later in San Ysidro , California , having been towed from the Mexican border . Did they cross over ? Surveillance video taken that night shows a family fitting the description of the McStays walking into Mexico . But it has never been confirmed it was them . Or , if it was , that they ever came back . Mike McStay , for one , says he does n't believe this video shows his brother . `` That 's certainly part of this huge puzzle , '' San Diego County Sheriff 's Department spokeswoman Jan Caldwell said of reports that the family crossed into Mexico and ate dinner and drank cocktails there . `` What happened here ? Was that part staged ? Did they actually cross into Mexico ? '' Caldwell added , `` We still think that there 's a strong possibility that they did . When did they come back ? Were they under duress ? I mean , these are all questions that we we want to find out . '' On February 15 , relatives called the sheriff 's department to report the family missing . At the home , there were eggs on the kitchen counter , bowls of popcorn in the living room , and two dogs . But no trace of the McStays . The next three years were filled with speculation , fear and hope . Rick Baker published a book , `` No Goodbyes , '' on their plight . Mike McStay and other family members tried to keep the case alive . Then came the call to the San Bernardino County Sheriff-Coroner Department around 10 a.m. on November 11 . A motorcyclist said he had spotted skeletal remains in a sandy , scrubby High Desert area between Quarry Road and Interstate-15 , the highway Angelenos take to get to and from Las Vegas . Otherwise , though , it could well have been considered the middle of nowhere -- some 105 miles north of the McStay 's hometown of Fallbrook , and 160 miles north of San Ysidro . Four days later , the sheriff 's identified the victims as the McStays . The San Bernardino Sheriff 's Department has deemed their deaths homicides , but it did not give a cause in order `` to protect the investigation . '' `` Every available resource will be utilized in this investigation to identify the suspects involved in this heinous crime and bring them to justice , '' said Sheriff John McMahon . Their bones gone , large crosses now mark the spot where the McStays ended up . Approaching their makeshift grave for the first time , Mike McStay said what he sees indicates to him that the guilty party knew what they were doing . `` You see how this is kind of sunken down ? '' he said . `` It gives you a little cover from the road . Somebody had to know the area , had to know you needed a four-wheel drive . '' Couple lost on snow-covered road writes goodbye letters , prepared to die . CNN 's Randi Kaye reported from north of Victorville , California ; CNN 's Greg Botelho reported and wrote this story from Atlanta .
McStay , his wife and their four boys were reported missing in February 2010 . Their car was found near the Mexican border ; their home offered few clues . A motorcyclist saw their remains February 2010 in desert about 18 miles from their home . Joseph McStay 's brother promises the family 's killers : `` We 're going to find you ''