It appears that archaeologists in Israel believe that they have found the tomb of the Biblical prophet Zechariah in Horbat Midras, the site of a Jewish community in Roman times, southwest of Jerusalem. According to Byzantine church and mosaic floor uncovered at Hirbet Madras:
A public building of impressive beauty dating to the Byzantine period, in which there are several construction phases, was exposed in the excavation. In the last two construction phases the building was used as a splendid church. However, based on the results of the excavation and as evidenced by the artifacts, it seems that this church is built inside a large public compound from the Second Temple period and the Bar Kokhba Revolt, which was used in the first construction phases of the compound.
The church, in its last phases, was built as a basilica, at the front of which is a large flagstone courtyard from which worshippers passed into an entry corridor. Through a shaped opening one enters into the nave where there were eight breathtaking marble columns that bore magnificent capitals which were specially imported from Turkey. At the end of the nave is a raised platform and on either side of the nave are two wide aisles.
All of the floors in the building were adorned with spectacular mosaic floors decorated with faunal and floral patterns and geometric designs that are extraordinarily well preserved. Located behind the platform are two rooms, one paved with a marble floor and the other that led to an underground tomb devoid of any finds. Branching out beneath the entire building is a subterranean hiding complex in which there are rooms, water installations, traps and store rooms. This complex belongs to the large building from the Second Temple period which the Byzantine church was built into. Among the artifacts discovered in the hiding complex are coins from the time of the Great Revolt (66-70 CE) and the Bar Kokhba Revolt (132-135 CE), stone vessels, lamps and various pottery vessels that are characteristic of the Jewish population from the community at that time.
So, on what basis do authorities believe that this is the tomb of Zechariah? Well, it isn't positive (hence, the question in the title), but it appears that there is some significant evidence:
As previously mentioned, researchers who visited the site are of the opinion that the site is the residence and tomb of the prophet Zechariah. Ancient Christian sources identified the burial place of the prophet Zechariah in the village of Zechariah, and noted that his place of burial was discovered in 415 CE. The researchers believe that in light of an analysis of the Christian sources, including the Madaba Map, the church at Hirbet Madras is a memorial church designed to mark the tomb of the prophet Zechariah. This issue will be examined and studied in the near future.
I personally look forward to reading more about this.