diff --git a/src/reboost/optmap/evt.py b/src/reboost/optmap/evt.py
index 5ce27493..ca83b137 100644
--- a/src/reboost/optmap/evt.py
+++ b/src/reboost/optmap/evt.py
@@ -3,10 +3,8 @@
 import logging
 from collections import OrderedDict
 from collections.abc import Generator, Iterable
-from pathlib import Path
 
 import numpy as np
-from lgdo import lh5
 from lgdo.lh5 import LH5Iterator
 from lgdo.types import Table
 
@@ -105,27 +103,6 @@ def _ensure_vert_df(vert_it: LH5Iterator, evtid: int) -> Generator[Table, None,
     assert had_last_chunk, "did not reach last chunk in optmap-evt building"
 
 
-def build_optmap_evt(
-    lh5_in_file: str, lh5_out_file: str, detectors: Iterable[str | int], buffer_len: int = int(5e6)
-) -> None:
-    """Create a faster map for lookup of the hits in each detector, for each primary event."""
-    lh5_out_file = Path(lh5_out_file)
-    lh5_out_file_tmp = lh5_out_file.with_stem(".evt-tmp." + lh5_out_file.stem)
-    if lh5_out_file_tmp.exists():
-        msg = f"temporary output file {lh5_out_file_tmp} already exists"
-        raise RuntimeError(msg)
-
-    for vert_it_count, chunk in enumerate(generate_optmap_evt(lh5_in_file, detectors, buffer_len)):
-        log.info("store evt file %s (%d)", lh5_out_file_tmp, vert_it_count - 1)
-        lh5.write(Table(chunk), name=EVT_TABLE_NAME, lh5_file=lh5_out_file_tmp, wo_mode="append")
-
-    # after finishing the output file, rename to the actual output file name.
-    if lh5_out_file.exists():
-        msg = f"output file {lh5_out_file_tmp} already exists after writing tmp output file"
-        raise RuntimeError(msg)
-    lh5_out_file_tmp.rename(lh5_out_file)
-
-
 def get_optical_detectors_from_geom(geom_fn) -> dict[int, str]:
     import pyg4ometry
     import pygeomtools
diff --git a/tests/test_optmap.py b/tests/test_optmap.py
index 1d9d08f8..6eaa1e01 100644
--- a/tests/test_optmap.py
+++ b/tests/test_optmap.py
@@ -13,7 +13,6 @@
     merge_optical_maps,
     rebin_optical_maps,
 )
-from reboost.optmap.evt import build_optmap_evt
 from reboost.optmap.optmap import OpticalMap
 
 
@@ -53,16 +52,6 @@ def tbl_hits(tmptestdir):
     return (str(hit_file),)
 
 
-def test_optmap_evt(tbl_hits, tmptestdir):
-    evt_out_file = tmptestdir / "evt-out.lh5"
-    build_optmap_evt(
-        tbl_hits[0],
-        str(evt_out_file),
-        detectors=("1", "002", "003"),
-        buffer_len=20,  # note: shorter window sizes (e.g. 10) do not work.
-    )
-
-
 @pytest.fixture
 def tbl_evt_fns(tmptestdir) -> tuple[str]:
     evt_count = 100