Would my testimony be considered incomplete or a false oath, and what is the position of Sharia law on this, and what expiation is incumbent upon me, after I concealed from the judge that the murderers passed through my house, knowing that I did not witness the crime myself?

A Muslim must bear witness for Allah Almighty if requested to do so, provided they are certain and do not fear for themselves, their property, their honor, or their family. This is based on Allah Almighty's saying: ﴿And bring to witness two just men from among you and establish the testimony for Allah﴾ [At-Talaq: 2], and His saying: ﴿And do not conceal testimony, for whoever conceals it - his heart is indeed sinful﴾ [Al-Baqarah: 283]. However, bearing witness is not obligatory if the witness fears harm, or if the ruler is unjust, or if the witness is not certain. If a Muslim is compelled to take an oath to ward off harm, there is no breaking of the oath. As for swearing an oath to rescue an oppressed stranger, it is commendable, and expiation is required. But if the person to be rescued is an oppressor, it is not permissible to conceal them or withhold testimony. Repentance is obligatory for an oath that was incorrect, and it is safer to offer expiation for an oath.